Electrophotographic processes for making photographic transparencies



June 1956 R. M. SCHAFFERT ELECTROPHOTOGRAPHIC PROCESSES FOR MAKING PHOTOGRAPHIC TRANSPARENCIES Filed Jan. 5, 1962 'IIIII'IIIIIIIIIIIIIIIIIIIA ATTORNEY United States Patent 3,254,997 ELECTROPHOTOGRAPHEC PROCESSES F012. MAK- ING PHOTGGRAPHIC TRANSPARENCIES Roland Michael Schaifert, Saratoga, Califl, assignor to International Business Machines Corporation, New

York, N.Y., a corporation of New York Filed Jan. 3, 1962, Ser. No. 164,014 Claims. (Cl. 96-1) with, for example, powder cloud development, it is difiicult to control the process in a manner that will provide the heavy deposit of powder in the background and still avoid some powder deposition in the image areas where transparency is desired. Furthermore, after development it is necessary to transfer the powder deposit from the electrophotographic plate to a transparent film. It is known that in electrostatic transfer only a portion of the powder layer is removed and transferred. Therefore, it is necessary to resort to more elaborate transfer techniques such as adhesive transfer. Even so, the negatives produced in this manner are usually unsatisfactory, resulting in areas and spots that are not sufiiciently opaque to provide good contrast.

An object of the invention is to provide processes and apparatus for making photographic transparencies by electrophotogr-aphic techniques with a minu-mum number of operative steps and expenditure of materials.

Another object is to produce electrophotographic negatives which are superior to those now possible with the present electrophotographic techniques.

Another object is to produce photorecords in the form of negatives by rapid processes.

The foregoing and other objects, features and advantages of the invention are attained in processes wherein the electrostatic image charge pattern of the electrophotographic plate, for example, a xerographic plate, is brought into virtual contact with a plastic film of normally transparent resin or polymer in which fine particles of opaque material are uniformly dispersed.

These particles, which may be of colloidal size, render the otherwise transparent film essentially opaque when dispersed in the film. Furthermore, these particles are dispersed and blended within the film material in such manner that each particle is electricaly charged. Upon liquifying the film, by heating or applying a solvent, the charged particles are free to move and can be either attracted or repelled by the charges of the electrostatic image on the electrophotographic plate. The mode of charge movement depends whether the original is positive or negative. Upon solidifying the film, the displaced particles are fixed in position, and a photographic negative is produced.

More specifically, one process according to the invention comprises laying a liquid film of transparent dielectric material containing uniformly dispersed opaque particles on a supporting surface element, bringing an image charged electrophotographic plate into contact with the liquid film effecting rearrangement of the particles in accordance with the charges making up the charge image on the plate, solidifying the film material, fixing the positions of the particles, and stripping or removing the resulting negative from the electrophotographic plate.

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Another more specific process according to the invention comprises transferring an electrostatic image to a solid film of meltable dielectric having opaque particles uniformly dispersed therein, heating the film to the melting point, bringing into contact with an image-bearing electrophotographic plate and effecting rearrangement of the opaque particles in accordance with the image charge pattern on the electrophotographic plate, solidifying the film, stripping or removing the film from the electrophotographic plate.

The polarity of the electric charges acquired by the particles dispersed in the film material will be determined by two factors:

(1) The polarity of the charge pattern on the electrophotographic plates.

(2) The type of original subject or document from which the negative is to be produced, i.e., Whether the original is photographically negative or positive.

For example, if the original is photographically positive and the charge pattern consists of electrically positive charges, the polarity of the particles dispersed in the film material must be positive, so that they will be repelled away from the charged areas of the image, i.e., the areas which are desired to be transparent in the film.

If the original is photographically negative, and the charge pattern electrically positive, then the particles must be negatively charged so that they will be attracted away from the areas that are to be transparent.

If the image charge pattern is electrically negative, the polarity requirements for the dispersed particles will be reversed from those given above.

Further, according to the invention an automatic and continuous mode of operation is realized in an arrangement wherein a rotating xerographic drum is partially immersed in liquid film material in which fine particles of the opaque material are dispersed. An image of a document to be reproduced is projected optically onto the electrophotographic drum according to known techniques to produce an electrostatic image charge pattern on the drum surface. As the charged drum passes through the liquid film material in which the particles are suspended, the drum picks up a thin film containing particles in pro portion to the nature and strength of the electrophotographic charge. The liquid photographic transparency film is then subjected to a mechanism for drying or chilling and the solidified film is stripped off the drum and wound on a conventional reel. I

In order that full advantage and elfect may be obtained in practice, the invention is described hereinafter in terms of preferred embodiments, given by way of examples only, with reference to the accompanying drawing forming a part of the specification, and in which:

FIG. 1 illustrates the essentials of apparatus and principal steps for performing a process according to the invention;

FIG. 2 illustrates apparatus for performing the processes of the invention in an automatic and continuous mode of operation; and

FIG. 3 depicts essentials of apparatus for carrying out an alternate process according to the invention.

FIG. 1 depicts the essentials of apparatus for carrying out a process according to the invention. On a transparent base support 8, a layer 10 of dielectric film material containing a suspension of opaque rendering colloidal particles is laid inliquid form. The liquid film may be a solid film layer of meltable plastic softened by heating or a soluble resin previously dissolved in a suitable solvent with dispersed particles therein. In the interest of clarity the thickness of the conductive base plate 8 and that of the film 10 are exaggerated; it being that the general case the film will be in the range of 1.0 to 20.0 microns thick.

' An electrophotographic plate as shown in FIG. lb comprising a conductive base plate 18, carrying a layer of photoconductive material 20 bearing an electrostatic image charge pattern corresponding to the image to be produced in the transparency, is brought into contact with the dielectric film as shown in FIG. 10. The particles suspended in the liquid dielectric become electrically charged. A description of such a suspension as used for liquid development of electrostatic images, is to be found in US. Patent 2,907,674. Further information will be found in an article entitled Xerography by K. A. Metcalfe and R. J. Wright and in the Oil and Colour Chemists Association Journal, vol. 9, pp. 845-856 for November 1956.

The dispersed particles, which in the case illustrated are electrically charged to positive polarity, are repelled by the positive electrostatic image charges and pushed away from the image areas and into the region of nonimage areas as shown in FIG. 1d.

The case is thus far illustrated in terms of positive image charges on the electrophotographic plate and positively charged opaque particles dispersed in the film material, with particle movement effected by charge repulsion. It should be clearly understood, however, that negative charges on one or both of the elements and charge attraction as well as charge repulsion are clearly within the command of those skilled in the art.

The electrophotographic plate is removed from the film 10' as shown in FIG. 1d preferably after the film 10' has been solidified by drying or chilling. The support base 8 is transparent, and may consist of glass or a flexible plastic such as polyethylene glycol terephthalate, or that more commonly known by the registered trademark, Mylar.

FIG. 2 is a schematic diagram of essentials of apparatus for carrying out the processes of the invention n an automatic and continuous mode of operation. The essentials only are shown in this illustration, it being understood that conventional methods and structures for transporting the various components of the apparatus, shielding the charged areas from light or electrostatic fields, and the like are readily apparent to those skilled in the art. Within a light tight housing 30, a rotatable electrophotographic drum 16 is partly immersed in a bath 10" of dielectric material containing finely dividing opaque particles in the form of a resin-solvent-pigment mixture or a meltable resin and a dispersed pigment. A lamp 34 is suitably arranged to discharge any residual charge on the photoconductive layer 20' of the drum 16' before uniform positive charge is given the photoconductive layer 20' by means of a corona charging unit 36 powered by a direct potential source 38. The image of a document 40, suitably exposed by means shown only as a pair of lamps 42, is optically projected by a system schematically illustrated by a symbolic lens 44 onto the photoconductive layer 20' to form an image charge pattern on the drum 16'. As the peripheral surface drum rotates into the bath 10", a film 10' containing the opaque particles arranged in accordance with the projected image adheres to the drum 16'. A blower 58 is arranged to dry the liquid film and if found desirable film chilling means may be included in the blower. The film 10 is guided over a drum 62 onto a take-up reel 64. It is only necessary that the initial leader of film 10' be separated and arranged on the guide roller 62 and reel 64 to part the film from the conductive surface layer 20' thereafter. A heater 66 is provided to keep the resin pigment mixture in the container 32 liquid, if required.

Examples of meltable resins for use in the process according to the invention are: ethylcellulose polyethylene, polyethylene-wax mixtures, polystyrene, acrylic resin such as that more commonly known by the registered trademark -Acryloid, and polystyrene-butadiene copolymers. These resins may be mixed with a solid solvent, such as a high melting point polyfiuorochloroalkane, such as that more commonly known by the registered trademark Freon, cyclohexane, toluene and similar solvents to reduce the melting point of'the mixture. Other nonmeltable resins, such as the methacrylates, vinyls, and the like, can be used when dissolved in a suitable solvent. Pigments, such as carbon black, iron oxides, lead chromate in paste form designated alkyd paste, titanium dioxide, lead chromate, and the various pigments used in printing inks are suitable for use as the dispersed particles in the resins. Those skilled in the art will readily prepare the above mentioned materials in known manner in accordance with the problem at hand. For example, a preferred dielectric material for forming the film is prepared by dissolving one gram of titanium dioxide in paste form designated TiO -linseed oil paste in one liter of toluene; dissolving 40% by weight of acrylic resin in one liter of toluene; and mixing the two together in equal parts. Another mixture is prepared by dispersing one gram of carbon black oil paste in one liter'of cyclohexane; dissolving thirty grams of polyethylene in seven hundred milliliters of cyclohexane; and mixing them together. Still another mixture is prepared by dispersing one gram of lead chromate paste-designated alkyd paste-in one liter of toluene; dissolving thirty-five grams of polystyrene in six hundred fifty milliliters of toluene; and mixing them together.

Any one of the above described mixtures may be used to form the film 10 described in connection with the arrangement shown in FIG. 1 and as the solution 10 in the tanks 32 shown in FIG. 2. These mixtures dry readily in air, and the drying is readily speeded for use in a machine as shown in FIG. 2 by the use of a blower 58. The film peels readily from any smooth metal surface, and in the care of a machine as shown in FIG. 2, once a leader is peeled off the remainder of the film peels off readily so thatstripping is no problem.

FIG. 3 illustrates an alternate process according to the invention. An electrostatic image is transferred to a solid film of the material described hereinbefore as shown in FIG. 3a. Film 10" is then heated until it becomes liquid, as shown by the film 1G in FIG. 3b. The film contracts in the charged-areas, and at the same time the particles are repelled away from the image areas leaving these areas essentially transparent. Heating is accomplished by means of a heater 68, preferably aided by a blower 58'. In this case, it is preferable that the base 8 be a transparent conductive material.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood that those skilled in the art will make other changes in the form and details without departing from the spirit and scope of the invention.

The invention claimed is: 1. A process of electrophotographic image reproduction, comprising the steps of bringing an electric charge image bearing surface element of an electrophotographic device into contact with a film of meltable transparent dielectric material having electrically charged opaque colloidal particles dispersed therein, heating said film of dielectric material to the melting point thereof for liquidizing the same, thereby releasing said electrically charged particles for rearrangement in accordance with the charge image, cooling said dielectric material to the solidification temperature thereof for reforming said film, and stripping thereformed film from said electrophotographic device, 1

thereby forming a photographic transparency. 2. A process of electrophotographic image reproduction comprising the steps of laying a liquid film of transparent dielectric material having electrically charged opaque colloidal particles dispersed therein on a supporting element,

bringing an electric charge image bearing surface element of an electrophotographic plate into contact with said liquid film,

thereby causing said particles to rearrange in accordance with the charge image, treating said dielectric material for soldi-fying said film, and stripping the solidified film from said electrographic plate,

thereby forming a photographic transparency. 3. A process of electrophotographic image reproduction, comprising the steps of converting transparent dielectric material having liquid and solid phases with opaque colloidal particles dispersed therein to the liquid phase with said particles electrically charged in suspension, bringing an electric charge image bearing surface element of an electrophotographic device into contact With said liquid,

thereby forming a film on said electrophotographic device with said particles arranged in accordance with the charge image, treating said dielectric material on said device for solidifying said liquid into a film, and stripping the solidified film from said device,

thereby forming a photographic transparency. 4. A process of electrophotographic image reproduction, comprising the steps of heating a meltable transparent dielectric material having opaque colloidal electrically charged particles dispersed therein for forming a liquid with said particles in suspension, bringing an electric charge image bearing surface element of an electrophotographic drum into contact with said liquid,

thereby forming a film on said electrophotographic drum with said particles arranged in accordance with the charge image,

heating said dielectric material to the melting point for forming a liquid film,

thereby releasing said particles for rearrangement in accordance with the charge image, cooling said dielectric material to the solidification temperature thereof for solidifying said liquid film, and stripping the solidified film from said electrophotographic plate,

thereby forming a photographic transparency.

References Cited by the Examiner UNITED STATES PATENTS 2,892,709 6/1959 Mayer --1.7 X 2,907,674 10/1959 Metcalfe et al. 951.7 X

OTHER REFERENCES Publication: Xerography by K. A. Metcalfe and R. J. Wright in the Oil and Colour Chemists Assn; Journal, vol. 9, pp. 845-856 for November 1956.

NORMAN G. TORCHIN, Primary Examiner. EVON C. BLUNK, Examiner.

D. D. PRICE, Assistant Examiner. 

1. A PROCESS OF ELECTROPHOTOGRAPHIC IMAGE REPRODTION, COMPRISING THE STEPS OF BRINGING AN ELECTRIC CHARGE IMAGE BEARING SURFACE ELEMENT OF AN ELECTROPHOTOGRAPHIC DEVICE INTO CONTACT WITH A FILM OF MELTABLE TRANSPARENT DIELECTRIC MATERIAL HAVING ELECTRICALLY CHARGED OPAQUE COLLOIDAL PARTICLES DISPERSED THEREIN, HEATING SAID FILM OF DIELECTRIC MATERIAL TO THE MELTING POINT THEREOF FOR LIQUIDIZING THE SAME, THEREBY RELEASING SAID ELECTRICALLY CHARGED PARTICLES FOR REARRANGEMENT IN ACCORDANCE WITH THE CHARGE IMAGE, COOLING SAID DIELECTRIC MATERIAL TO THE SOLIDIFICATION TEMPERATURE THEREOF FOR REFORMING SAID FILM, AND STRIPPING THE REFORMED FILM FROM SAID ELECTROPHOTOGRAPHIC DEVICE, THEREBY FORMING A PHOTOGRAPHIC TRANSPARENCY. 